This study is a follow-up trial for those subjects in actg 302 and 303 who were subsequently randomized to receive either new rti monotherapy agents (d4t) or the addition of 3tc/3tc placebo featured in different nucleoside analogue combination regimens. The primary goals outlined in these trials were to carefully characterize subjects who have a well defined nucleoside exposure history with respect to their symptomatis state, their cd4 count trajectory, and their virologic profile and to relate this to the response to new antiretroviral interventions in HIV infected patients who have been treated either with respect to their symptomatic state, their cd4 count trajectory, and their virologic profile, and to relate this to the response to new antiretroviral interventions in HIV infected patients who had been treated either with monotherapy (zdv or ddi) or dual combination therapy (zdv/ddi or zdv/ddc) while participating in actg 175. The 302/303 trials feature 10 different combination drug regimens using d4t, zdv, ddi, ddc and 3tc. Patients from actg 302/303 will be provided at least 1, and if possible, 2 new rti's when initiating study drug therapy in this rollover trial. Actg 303 featured 3 treatment arms which included 3tc/zdv: zdv/ddi/3tc, zdv/dddc/3tc, or zdv/3tc. Actg 302 had 2 treatment arms that included 3tc/zdv combination:zdv/3tc or zdv/ddi/3tc. These patients have prolonged zdv, 3tc and ddl or ddc exposure which limits the available options to provide 2 new rtis to these subjects. All patients will be assigned to receive open label rti therapy in this trial which will consist of ddl/4dt, 3tc/d4t or ddl/3tc dual nucleoside analogue combination regimens. Thus all the subjects participating in this trial will, if their baseline plasma HIV RNA level as >/- 500 copies/ml, have a switch in rrti therapy to either ddl/d4t or ddl/3tc. The potency of these new rti regimens may be influenced by the prior development of drug resistance to earlier rtis that each subject received in actg 175 and then in either actg 302 or 303.